1. Field of the Invention
The present invention relates to an optical semiconductor device and a method of fabricating an optical semiconductor device and, more specifically, relates to an optical semiconductor device using Be as a p-type dopant, and Fe as a dopant for making current blocking layers highly resistive and a method of fabricating such an optical semiconductor device.
2. Description of the Related Art
In recent years, the amount of information handled by information communication devices has become enormous and, particularly in the field of optical communications, there has been increasing need for semiconductor light-emitting devices. (semiconductor laser, modulator, laser with modulator, etc.) enabling ultra-high-speed modulation exceeding 40 GHz and ultra-high-speed semiconductor light-receiving devices (photodiode etc.) exceeding 80 GHz for receiving modulated lights coming from light-emitting devices through optical transmission lines.
Such a semiconductor light-emitting device or semiconductor light-receiving device (hereinafter collectively referred to as an “optical semiconductor device”) comprises, in addition to electrodes, a semiconductor having a p-type or n-type conductivity for supplying the power to the device. Further, in order to enable high-speed modulation exceeding 40 GHz, it is necessary to reduce the device resistance or capacitance. For this purpose, there has been adopted a method of limiting a region where current as a feed to the device flows, such as providing Fe—InP current blocking layers in the optical semiconductor device.
The Fe—InP current blocking layers are usually disposed on both sides of the p-type semiconductor of the optical semiconductor device so as to be in contact with the p-type semiconductor. In the case of such a structure, however, it is easy to occur that Fe of the Fe—InP current blocking layers may interdiffuse with the p-type dopant (e.g. Zn, Be, or Mg) of the p-type semiconductor. When the interdiffusion occurs between Fe and the p-type dopant as described above, the resistance of each Fe—InP current blocking layer decreases near an interface between itself and the p-type semiconductor. In this case, there arises a problem that the function of the Fe—InP current blocking layers, such that the region where the current flows is limited by providing the highly resistive Fe—InP current blocking layers on both sides of the p-type semiconductor, is not efficiently achieved.
In view of this, as a countermeasure, there are considered methods each for preventing Fe from interdiffusing with the p-type dopant of the p-type semiconductor.
As one of such methods, there is, for example, the method of doping Fe, simultaneously with the p-type dopant, into a p-type semiconductor contacting Fe—InP current blocking layers (e.g. see Japanese Patent No. 3257045).
Further, there is the method of employing Ru—InP current blocking layers instead of Fe—InP current blocking layers (e.g. see Jpn. J. Appl. Phys. vol. 42 (2003), pp. 2320–2324).
As a p-type dopant doped into a p-type semiconductor, Zn is often used particularly in the MOCVD (Metal-Organic Chemical Vapor Deposition) method. However, since the diffusion coefficient of Zn is relatively large, Zn may diffuse into an active layer. In view of this, there is concern that the luminous efficiency of a semiconductor laser is lowered and therefore a suggestion has been proposed using, instead of Zn, a material having a small diffusion coefficient such as Be (e.g. see JP-A-H08-102567).
However, when Be is used as a dopant of a p-type semiconductor, even if attempting to dope Be and Fe simultaneously, doping delay may occur with respect to Be. Therefore, it is considered to be difficult to simultaneously dope Fe and Be into a semiconductor by the use of the conventional method.